It is known to dispense rolled-sheet material, such as waxed paper, metal foil, and the like from a rectangular container through an elongated opening. To facilitate the tearing or severing of a segment of sheet material dispensed from the container, one edge of the opening in the container usually has conventional tooth means. Generally, the tooth or severing means comprises an enlongated cutter bar having a plurality of spaced-apart conventional cutting teeth. This cutting bar is secured to an edge disposed proximal the opening in the container so that segments of the sheet material dispensed through the opening could be quickly and easily severed from the roll. The low tear strength of many of these conventional sheet materials required only a slightly sharp edge.
The advent of plastic film for consumer use as household food wraps has produced various plastic films having high strength and stretch characteristics. These new plastic films were unsuitable for conventional severing means employing slightly sharp edges and therefore cutter bars with sharp points or sharp side edges were contemplated. To be suitable for consumer use these devices usually required a guard or other safeguard means to protect a user from injury. In addition, the cost of these cutter bars and protection means are relatively high when compared to the overall cost of the dispenser in which the film is packed, thus rendering them economically unsuitable for consumer use.
Of the new household food wraps on the market, high stretch capability and high strength have been found to be desirable characteristics which render the wraps ideally suited for household consumer use. Thus the desirable properties of film-type food wraps include the following:
1. "Cling"--how well the film stays wrapped around food such as sandwiches and adheres to open containers for food such as glass bowls.
2. High strength characteristics such as tensile strength, puncture resistance and Elmendorf tear.
3. High stretch capability--how readily the film may be stretched and elongated without breakage.
4. Good handleability--how well the film resists tangling during use.
5. "Cutter bar tear"--how easily a length of the film may be withdrawn from a carton and severed by ripping or cutting on the carton's cutter bar.
The cling property is typically enhanced by the use of cling additive(s) in the film. Also, the film-type food wraps are customarily produced in thin gauges such as 0.5 mil in thickness, for economy and to provide a limpness so that the film may conform to the various shapes of packaged or wrapped containers, bowls and foods. With such thin film, toughness becomes a problem and manufacturers of film-type food wraps are constantly seeking to improve this property.
Consumers are also interested in the ease of dispensing and tearing off a sheet of film as it is withdrawn from the container that the film is packaged in. For this purpose, containers such as cartons are ordinarily provided with sharp edges, usually, a saw-tooth edge, known as a cutter bar. Manufacturers have attempted to comply with this consumer demand by supplying film that can be withdrawn from a container to a desired length and severed along the cutter bar with ease.
With the introduction of "linear" low density polyethylene made by low pressure processes (hereinafter referred to as "LPLDPE"), attempts have been made to substitute this material for cling wrap film applications in place of conventional highly branched low density polyethylenes made by high pressure processes (hereinafter referred to as "HPLDPE"). The reason for these efforts is that LPLDPE is widely recognized as being tougher and stronger than HPLDPE (reference: "Process Engineering News", February 1980, pg. 33). However, it has been determined that typical film grade LPLDPE does not provide one of the important properties required in cling wrap plastic films--ease in cutter bar tear off. Even at 0.5 mils thickness, LPLDPE film is very difficult and in some instances impossible to tear off in the transverse direction of the film on conventional cutter bar strips. The film tends to elongate, and considerable effort and energy are required to sever the film.
Other tough, stretchy plastic films, such as ethylene copolymers and terpolymers, and plasticized vinyls, are also difficult or impossible to tear on conventional cutter bars. It is also well known to the art that high pressure polyethylenes can be given increased stretch and toughness by blending them with other polymers such as ethylene vinyl acetate.
Suitable cling-wrap polyethylene film is disclosed in U.S. patent application Ser. No. 264,092 filed on May 15, 1981 in the name of E. N. Biel. The disclosure in this application is incorporated herein by reference. Although this disclosure recommends the use of low pressure-low density polyethylene in the range of between about 5 and about 16 weight percent of the LPLDPE plus HPLPDE total weight, higher amounts of LPLDPE can be employed to increase the strength and stretchability of the film for use in a wide range of applications.
It is an object of the present invention to provide a blade having a plurality of spaced-apart sharp cutting teeth disposed below and between a plurality of spaced-apart projected blunt members that is ideally suited for use in the safe severing of sheet material such as stretch film.
Another object of the present invention is to provide a blade ideally suited for severing plastic film having high strength characteristics and high stretch capability.
Another object of the present invention is to provide a blade ideally suited for use as a severing means adapted to be attached proximal an elongated opening in a rectangular container housing a roll of sheet material.
Another object of the present invention is to provide a blade for severing tough, stretchy, or tear resistant films, which has a build-in safety means to protect against accidental injury to the user.
Other features and advantages of this invention will be apparent from the following description taken in conjunction with the accompanying drawings.